heavier crop of wheat is produced
than without the intercalation of clover. What, it may be asked, is the
explanation of this apparent anomaly?

"In taking up this inquiry, I was led to pass in review the celebrated
and highly important experiments, undertaken by Mr. Lawes and Dr.
Gilbert, on the continued growth of wheat on the same soil, for a long
succession of years, and to examine, likewise carefully, many points, to
which attention is drawn, by the same authors in their memoirs on the
growth of red clover by different manures, and on the Lois Weedon plan
of growing wheat. Abundant and most convincing evidence is supplied by
these indefatigable experimenters, that the wheat-producing powers of a
soil are not increased in any sensible degree by the liberal supply of
all the mineral matters, which enter into the composition of the ash of
wheat, and that the abstraction of these mineral matters from the soil,
in any much larger proportions than can possibly take place under
ordinary cultivation, in no wise affects the yield of wheat, provided
there be at the same time a liberal supply of available nitrogen within
the soil itself. The amount of the latter, therefore, is regarded by
Messrs. Lawes and Gilbert, as the measure of the increased produce of
grain which a soil furnishes.

"In conformity with these views, the farmer, when he wishes to increase
the yield of his wheat, finds it to his advantage to have recourse to
ammoniacal, or other nitrogenous manures, and depends more or less
entirely upon the soil, for the supply of the necessary mineral or
ash-constituents of wheat, having found such a supply to be amply
sufficient for his requirements. As far, therefore, as the removal from
the soil of a large amount of mineral soil-constituents, by the
clover-crop, is concerned, the fact viewed in the light of the
Rothamsted experiments, becomes at once intelligible; for,
notwithstanding the abstraction of over 600 lbs. of mineral matter by a
crop of clover, the succeeding wheat-crop does not suffer. Inasmuch,
however, as we have seen, that not only much mineral matter is carried
off the land in a crop of clover, but also much nitrogen, we might, in
the absence of direct evidence to the contrary, be led to suspect that
wheat, after clover, would not be a good crop; whereas, the fact is
exactly the reverse.

"It is worthy of notice, that nitrogenous manures, which have such a
marked and beneficial effect upon wheat, do